The application of such a high-voltage power transistor that is made of SiC (silicon carbide), GaN (gallium nitride) and the like in a power switching unit is expanding rapidly. However, since the power transistor is generally a switching element which is normally on by default, the application of a gate driving circuit (gate driving circuit engaging in a normally-off operation), which is commonly used in the power switching unit to drive a switching element which is normally off by default, is impossible.
Thereby, in order to cause a switching element which is normally on by default to perform the normally-off operation, a cascode circuit may be configured in such a way that a drain of a normally-off switching element is connected to a source of a switching element which is normally on by default. In the case where the cascode circuit has such a configuration, when a switching element which is normally on by default is caused to perform a turn-off operation by the gate driving circuit engaging in a normally-off operation, it is possible to make it fall into an off state in the same way as a switching element which is normally off by default.